52. Counting unique values

A newspaper reached out to Bindle asking how many categories they have in the library?

In the previous lesson, our SQL toolbox grew by one more item – DISTINCT. It allows us to select unique column values or unique combinations in the case of several columns.

This lesson asks a more complex question – we need to count unique values. As we already know we can use the aggregate function COUNT to count records:

SELECT COUNT(genre) FROM books

☝ This query still returns the total number of books, since we just counted genres for each book.

To count...

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-- Type your query here, for example this one -- lists all records from users table: SELECT * FROM users
LIMIT 500
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